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This grey to brown-red ‘scribble-lichen’ grows on sheltered, moist calcareous rocks and should be collected for certain identification. It can be mistaken for O. calcarea, the most common lichen of the group to grow on stone. Apart from the damper habitat (for example, the shady clints in limestone pavement), longer spores and brown pigmentation of the disc tissues (microscope), the discs are also longitudinally furrowed and sometimes twisted into spiralling shapes. This is the limestone equivalent of O. saxigena on acid rocks. Northern and western Ireland.

Key characteristics

Very like O. calcarea but restricted to damper, shadier habitats such as recesses and underhangs in limestone etc.

Spores longer than in O. calcarea (22-30ųm), discs sometimes twisted or coiled, often with longitudinal furrows.